# How to plot constants as limit lines

Question asked by JERRY_MARKETOS on Jan 30, 2004
Latest reply on Sep 17, 2013 by lb19
How to plot constants as limit lines:

Sometimes we may desire to plot a constant value on a graph,
to be used as a visual limit line.  There are different ways to do this:

a)You can set artificial optimization or yield limit lines for the
desired limits you wish to display, and these will appear on
the relevant graphs.  (Right-click the Yield or Optimization folder...)

b)We can use equations, but we'll have to apply a little strategy:

If you start out by defining an equation variable such as  var1=?2
and then in a graph tell it to graph  (instead of S21 etc.)
by entering  =var1

...GENESYS will yell at you that var1 is not frequency dependent
(ie. swept) data, and won't display it.  So we apply a little strategy,
and do the following:

In equations, enter the following:

var1=freq/freq
var2=?2
var3=var1-1+var2

Now let's review what happens with the above:

The variable FREQ exists internally; FREQ represents the value
of the linear sweep frequency (in MHz).  Dividing FREQ by itself
just gives us a result that is always numerically equal to 1,
but GENESYS now recognizes var1 as a swept variable because it
is derived from a frequency dependent entity.

var2 is the variable that we will tune to adjust our limit line - read on...

var3 utilizes var1 (to obtain our swept data) and subtracts 1 from it,
which results in a zero value that is recognized as swept data.  We then
add the value of var2, which shifts that zero value as desired by the user.
The result is a var3 that can be used on a graph, and will vary according
to the value entered by the user for var2.

On the graph, enter a measurement =var3

The = sign tells GENESYS to get this from equations.

=================================================================================
(On a slightly different topic, note that you can create frequency dependent
variables by doing the above.  Note that FREQ is already defined -
just use FREQ, such as:

inductive_reactance=2*PI*FREQ*1E6*L

Where L is the inductance (defined somewhere else, in Henries).
Note that FREQ is held internally in MHz, so the 1E6 is used to convert to Hz.